Molecular Engineering of Carboxylated Polysulfone Membranes for Enhancing Salt Rejection

Developing advanced polysulfone (PSF) membranes for water treatment has garnered significant attention. However, carboxylated polysulfone membranes have shown limited rejection of various ions. This study explores four novel methods for modifying carboxylated polysulfone membranes to enhance their performance: (a) crosslinking of the dicarboxylated membrane surface with polyethylenimine or ethylenediamine, (b) partial hydrolysis of ethylenediamine-crosslinked dicarboxylated membranes to create tailored pores and surface brushes with terminal amine groups, (c) attachment of alkyl brushes to the dicarboxylated membrane surface, and (d) formation of quaternary ammonium moieties at the membrane surface. All modified membranes were fully characterized, and their enhanced functionality was confirmed. For instance, the PSF-PEI membrane exhibited a 28% CaCl₂ rejection and PSF-NH₂ showed improved CaCl₂ rejection up to 37%, compared to 0% for the unmodified PSF-COOH. These methods present practical strategies to modify carboxylated-related membranes further, offering potential pathways to enhance their performance.